Metal halide perovskites (MHPs) have numerous advantages as light emitters such as high photoluminescence quantum efficiency with a direct bandgap, very narrow emission linewidth, high charge‐carrier ...mobility, low energetic disorder, solution processability, simple color tuning, and low material cost. Based on these advantages, MHPs have recently shown unprecedented radical progress (maximum current efficiency from 0.3 to 42.9 cd A−1) in the field of light‐emitting diodes. However, perovskite light‐emitting diodes (PeLEDs) suffer from intrinsic instability of MHP materials and instability arising from the operation of the PeLEDs. Recently, many researchers have devoted efforts to overcome these instabilities. Here, the origins of the instability in PeLEDs are reviewed by categorizing it into two types: instability of (i) the MHP materials and (ii) the constituent layers and interfaces in PeLED devices. Then, the strategies to improve the stability of MHP materials and PeLEDs are critically reviewed, such as A‐site cation engineering, Ruddlesden–Popper phase, suppression of ion migration with additives and blocking layers, fabrication of uniform bulk polycrystalline MHP layers, and fabrication of stable MHP nanoparticles. Based on this review of recent advances, future research directions and an outlook of PeLEDs for display applications are suggested.
Recent progress in understanding the origins of the low stability of metal halide perovskite (MHP) materials and light‐emitting diodes (PeLEDs) is reviewed. Various strategies to overcome the low stability are discussed with a special focus on the MHP material stability and operational stability of the PeLEDs. Future research directions to improve the stability are also suggested.
Ruddlesden–Popper phase (RP‐phase) perovskites that consist of 2D perovskite slabs interleaved with bulky organic ammonium (OA) are favorable for light‐emitting diodes (LEDs). The critical limitation ...of LED applications is that the insulating OA arranged in a preferred orientation limits charge transport. Therefore, the ideal solution is to achieve a randomly connected structure that can improve charge transport without hampering the confinement of the electron–hole pair. Here, a structurally modulated RP‐phase metal halide perovskite (MHP), (PEA)2(CH3NH3)m−1PbmBr3m+1 is introduced to make the randomly oriented RP‐phase unit and ensure good connection between them by applying modified nanocrystal pinning, which leads to an increase in the efficiency of perovskite LEDs (PeLEDs). The randomly connected RP‐phase MHP forces contact between inorganic layers and thereby yields efficient charge transport and radiative recombination. Combined with an optimal dimensionality, (PEA)2(CH3NH3)2Pb3Br10, the structurally modulated RP‐phase MHP exhibits increased photoluminescence quantum efficiency, from 0.35% to 30.3%, and their PeLEDs show a 2,018 times higher current efficiency (20.18 cd A−1) than in the 2D PeLED (0.01 cd A−1) and 673 times than in the 3D PeLED (0.03 cd A−1) using the same film formation process. This approach provides insight on how to solve the limitation of RP‐phase MHP for efficient PeLEDs.
Ruddlesden–Popper phase (RP‐phase) perovskites are promising materials for optoelectronic devices. Efficient RP‐phase perovskite light‐emitting diodes (PeLEDs) are developed by introducing a structurally modulated RP‐phase metal halide perovskite (MHP) emitter to increase the charge transport ability without hampering the confinement of the electron–hole pair. This approach provides insight on how to solve the limitation of RP‐phase MHP for efficient PeLEDs.
MXenes constitute a rapidly growing family of 2D materials that are promising for optoelectronic applications because of numerous attractive properties, including high electrical conductivity. ...However, the most widely used titanium carbide (Ti3C2Tx) MXene transparent conductive electrode exhibits insufficient environmental stability and work function (WF), which impede practical applications Ti3C2Tx electrodes in solution‐processed optoelectronics. Herein, Ti3C2Tx MXene film with a compact structure and a perfluorosulfonic acid (PFSA) barrier layer is presented as a promising electrode for organic light‐emitting diodes (OLEDs). The electrode shows excellent environmental stability, high WF of 5.84 eV, and low sheet resistance RS of 97.4 Ω sq−1. The compact Ti3C2Tx structure after thermal annealing resists intercalation of moisture and environmental contaminants. In addition, the PFSA surface modification passivates interflake defects and modulates the WF. Thus, changes in the WF and RS are negligible even after 22 days of exposure to ambient air. The Ti3C2Tx MXene is applied for large‐area, 10 × 10 passive matrix flexible OLEDs on substrates measuring 6 × 6 cm. This work provides a simple but efficient strategy to overcome both the limited environmental stability and low WF of MXene electrodes for solution‐processable optoelectronics.
Recently, various applications of MXenes have been intensively explored, except for optoelectronics, in which poor environmental stability severely impedes their practical application. This work provides a simple but effective approach to develop an environmentally stable MXene electrode that exhibits a high work function of 5.84 eV and distinguished solution processibility as the electrode for large‐area organic light‐emitting diodes.
Conventional organic light‐emitting devices without an encapsulation layer are susceptible to degradation when exposed to air, so realization of air‐stable intrinsically‐stretchable display is a ...great challenge because the protection of the devices against penetration of moisture and oxygen is even more difficult under stretching. An air‐stable intrinsically‐stretchable display that is composed of an intrinsically‐stretchable electroluminescent device (SELD) integrated with a stretchable color‐conversion layer (SCCL) that contains perovskite nanocrystals (PeNCs) is proposed. PeNCs normally decay when exposed to air, but they become resistant to this decay when dispersed in a stretchable elastomer matrix; this change is a result of a compatibility between capping ligands and the elastomer matrix. Counterintuitively, the moisture can efficiently passivate surface defects of PeNCs, to yield significant increases in both photoluminescence intensity and lifetime. A display that can be stretched up to 180% is demonstrated; it is composed of an air‐stable SCCL that down‐converts the SELD’s blue emission and reemits it as green. The work elucidates the basis of moisture‐assisted surface passivation of PeNCs and provides a promising strategy to improve the quantum efficiency of PeNCs with the aid of moisture, which allows PeNCs to be applied for air‐stable stretchable displays.
An air‐stable stretchable display consisting of an intrinsically stretchable electroluminescent device and perovskite nanocrystal (PeNCs) stretchable color conversion layer is proposed. Surprisingly, the increase in photoluminescence intensity of PeNCs in the water is proved to be caused by the surface passivation of moisture, which overcomes the water instability of perovskite materials.
The western conifer seed bug (WCSB) Leptoglossus occidentalis (Heidemann) (Heteroptera: Coreidae) is a pest insect that causes significant losses of coniferous trees worldwide. In this study, we ...sought to project the potential distribution of the WCSB based on dual CLIMEX modeling and random forest (RF) analysis to obtain basic data for WCSB monitoring strategies. The CLIMEX model, a semimechanistic niche model that responds to climate‐based environmental parameters, is a species distribution model that focuses on regional climatic suitability. Given that this model can be used to select areas that are likely to reflect the climatically favorable spread of species, which we initially used CLIMEX to evaluate the potential distribution of the WCSB. The RF algorithm was used to predict the potential occurrence of WCSB and to evaluate the relative importance of environmental variables for WCSB occurrence. Using the RF model, land cover was found to be the most important variable for classifying the presence/pseudo‐absence of the WCSB, with an accuracy of 77.1%. Climatic suitability for the WCSB was predicted to be 2.4‐fold higher in Southern Europe than in Western Europe, and the WCSB was predicted to occur primarily near coniferous forests. Given that CLIMEX and RF analyses yielded different prediction results, using the findings of both models may compensate for the shortcomings of these models when used independently. Consequently, to ensure greater prediction reliability, we believe that it would be beneficial to base predictions on the combined potential distribution data obtained using both modeling approaches.
This study developed an ensemble model with a dual modeling of a mechanistic model (CLIMEX) and a machine learning model (random forest). The developed models showed a reliable prediction of the potential distribution of Leptoglossus occidentalis in Europe in response to climate change.
Laser-assisted machining involves machining a workpiece after softening it with laser-emitted heat. Compared with conventional machining, laser assisted milling is a green manufacturing method, ...because it saves energy by reducing the cutting force. This paper examines cutting force and preheating temperature prediction for laser-assisted milling. Inconel 718 and AISI 1045 steel are employed in the experiments. The absorptivity of Inconel 718 was determined by conducting preheating experiments using a high power diode laser. Equations for determining cutting force and preheating temperature in laser-assisted milling are proposed using statistical analysis and regression analysis. The proposed equations are verified experimentally under a wide range of machining conditions. The cutting force and preheating temperature are measured using a tool dynamometer and a pyrometer, respectively. The results of this study can be applied to similar type of thermally assisted machining.
Bimetallic structures manufactured by direct deposition have a defect due to the sudden change in the microstructure and properties of dissimilar metals. The laser metal deposition (LMD)-wire arc ...additive manufacturing (WAAM) process can alleviate the defect between two different materials by depositing the functionally graded material (FGM) layer, such as a thin intermediate layer using LMD and can be used to fabricate bimetallic structures at high deposition rates with relatively low costs using WAAM. In this study, the LMD-WAAM process was performed, and the microstructure of the fabricated bimetallic structure of IN625-SUS304L was investigated. The microstructure of the FGM zone of the LMD-WAAM sample was mainly fine equiaxed dendrite morphologies. In contrast, coarse columnar dendrite morphologies constituted the WAAM zone. The composition of the major alloying elements of the LMD-WAAM sample gradually changed with the height of the deposited layer. The microhardness of the LMD-WAAM sample tended to increase with an increasing Inconel content. In the case of the LMD-WAAM sample, the fracture occurred near the interface between 25% IN625 and 0% IN625; in the WAAM sample, the final fracture occurred in SUS304L near the interface. The tensile strength of the LMD-WAAM samples was inversely proportional to the laser power. The results showed that the LMD-WAAM samples had 8% higher tensile strength than the samples fabricated using only WAAM.
In underwater laser beam machining (ULBM), water provides a cooling effect by reducing the influence of the laser heat source, which makes ULBM more suitable for marking, cutting, and postprocessing ...than laser beam machining (LBM). Because the laser heat source not only affects the substrate temperature, but also heats the water, this study analyzes how the cooling effect occurs when water is heated. In this study, the heat-transformed zones in ULBM and heated underwater laser beam machining (HULBM) were improved by approximately 33% and 24%, respectively, compared to LBM at 400 W. In addition, the heat-affected zones in ULBM and HULBM improved by approximately 15% and 9%, respectively, compared to LBM. The hardness of ULBM and HULBM was higher than that of LBM. Based on these results, it was confirmed that water can reduce the effect of the laser heat source and improve the mechanical properties. Experiments will be conducted on the underwater laser beam machining of various substrates, such as Inconel718 and Ti-6Al-4V, in a future study. In addition, experiments will be conducted on the underwater laser beam machining of various substrates using a cooling system that can lower the temperature of water.
Due to its regulation of CDK1/2 phosphorylation, WEE1 plays essentially roles in the regulations of G2/M checkpoint and DNA damage response (DDR). WEE1 inhibition can increase genomic instability by ...inducing replication stress and G2/M checkpoint inactivation, which result in increased cellular sensitivity to DNA damaging agents. We considered an increase in genomic instability induced by WEE1 inhibition might be used to augment the effects of drugs targeting DNA repair protein. Typically, PARP inhibitors are effective in germline BRCA 1/2 mutated breast and ovarian cancer, but their applicabilities in triple-negative breast cancer (TNBC) are limited. This study was conducted to investigate the anti-tumor effects of the WEE1 inhibitor, AZD1775, and the mechanism responsible for its potentiation of sensitivity to olaparib (a PARP inhibitor) via the modulation of DDR in TNBC cells. Our results suggest that AZD1775 could be used to broaden the application range of olaparib in TNBC and provide a rationale for a clinical trial of combined olaparib and AZD1775 therapy.
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